Effective Weed Control in Tea by Glyphosate¹

Glyphosate [JV-(phosphonomethyl) glycine] is a new post-emergence herbicide proven effective for control of perennial grass weeds. Several field and pot-cultures experi-ments were conducted to determine the effect of glyphosate on a wide range of weed species, the effect of surfactant and fertilizer materials on glyphosate activity, and synergism between glyphosate and 2, 4-D. Glyphosate effectively controlled perennial grass weeds such as Imperata cylindrica (L.) Beauv., Paspalum conjugatutm Berg., Paspalum scrobicula-tum L., Arundinella bengalensis (Spreng) Druce., and Selaria palmifolia (Koen.) Stapf. at rates ranging from 0.4 to 2.4 kg/ha. Glyphosate was also found effective on broadleaf weeds like Borreria hispida (L) K. Schum.. Polygonum chinense L., and Commelina benghalensis L., Addition of Triton AE, a wetting and sticking agent, has no effect on glyphosate activity. It, however, reduced rainwash of glyphosate off weed foliage occurring 1 or 2 hr after herbicide application. Trition AE had no effect if the rainfall was delayed by 4 hr or more after glyphosate application. Addition of ammonium sulphate upto 6 kg/ha enhanced the rate of glyphosate activity. Application of 2, 4-D as a tank mix with glyphosate enhanced the rate of activity of the latter. This synergistic effect helped reduce the rate of application of glyphosate substantially for effective weed control. The combina-tion of glyphosate and 2, 4-D was found very promising for two reasons: (a) activity of glyphosate was enhanced, and (b) in a mixed weed population, 2, 4-D can control most broadleaf weeds, and glyphosate can eliminate persistent grass weeds and some broadleaf weeds.